Cells of the nervous system, in vivo and in culture, and cells of the adrenal medulla, will be studied by electron microscopy and cytochemistry to gain insight into several problems related to the circulation of membranes between intracellular compartments and the cell surface (phenomena of exocytosis, endocytosis, lysosomal digestion, and packaging of secretory materials) and into the origin and fate of synaptic vesicles and of the related catecholamine-containing granules of the medulla. The work will focus on roles of Golgi apparatus, endoplasmic reticulum, lysosomes, and peroxisomes in the functioning of neurons, medulla cells and satellite and Schwann cells. These cells and organelles will be studied under varying physiological and pathological conditions such as during intensive synaptic activity or during the regranulation of adrenaline producing medulla cells after depletion induced by insulin. The studies should help fill important gaps in current understanding of the relations of structure and function in the nervous system.